docs: def io_loop(self):
          """Access the :class:`tornado.ioloop.IOLoop` instance for the
          current message.
  
          .. versionadded:: 3.18.4
  
          :rtype: :class:`tornado.ioloop.IOLoop` or :data:`None`
  
          """
          if self._message and self._message.connection:
              return self._connections[self._message.connection].io_loop